As a conventional small-sized projection device, there have been known projectors employing an optical modulator such as DMD (Digital Micromirror Device; produced by U.S. Texas Instruments Incorporated) and a liquid crystal element. A system which enlarges and projects images to be displayed with the optical modulator is called a microdisplay system. In microdisplay projectors, an illumination optical system and a projection optical system become large in size in order to project a two-dimensional image, which restricts the downsizing of devices.
On the other hand, development of what is called a laser scanning projector has been prosperous, in recent years. An laser scanning system is a system to project (display) an image on a scan surface by deflecting a laser beam emitted by a light source with a small mirror such as a MEMS (Micro Electro Mechanical Systems) mirror while modulating output of the laser beam, and by scanning the scan surface. A laser scanning projector exhibits various advantages as followings, which enables to downsize the entire device: (1) a scanning mirror is smaller in size than DMD; (2) since a laser light source is employed as a light source and a laser beam is simply emitted to a scanning mirror, an illumination optical system becomes smaller in size, too; and (3) since the scan surface is simply scanned with a spot (a light spot), a projection optical system becomes smaller in size, too.
Small-sized projection devices employing the laser scanning system have been disclosed in Patent Literatures 1 and 2, for example. In these projection devices, a galvanometer mirror and a MEMS mirror are employed as an optical scanning means to obliquely project a light flux from the optical scanning means to a screen. By driving the galvanometer mirror and MEMS mirror to cause their resonance, these mirrors can be driven at high speed with large amplitude (mechanical deflection angle), to scan a scan surface. Further, when a light beam is obliquely projected to shift a scanned image upward, the scanned image can be displayed at a position easily viewed by observers. Furthermore, when a scanning image display apparatus equipped with a projection device is placed on a table, a scanned image can be fully displayed on a projection area without being displayed on the table.
Patent Literature 1: JP-A No. 2006-178346
Patent Literature 2: JP-A No. 2005-234157